Tell me about it, I've been moving a baby seat back and forth from my '8 to an S4 back and forth this week and it's doing my head in as mine doesn't have ISOFIX because of the reclining rear seats. I suppose you'd get quicker at it after a while but have grazed knuckles from it. 
I know people that have retrofitted it to an S4 in the past.
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2009 Audi RS 6 Saloon V10 - 420mm Ceramics, Keyless, Soft Close, Adaptive Cruise, Glass Sunroof, Blinds, Twin Pane & UV, Freeview & DAB, High Beam Assist, MTM bits, Audi Exclusive Bits, MRC, Milltek, GYEF1 ASY2's, Bluetooth streaming music to AMI mod - 753 PS/1021 NM
2016 Audi S3 Saloon, Sepang, S-Tronic - B&O, Tech Pack etc... Company Car
1995 Audi A8 4.2 V8 quattro Sport - Bose, Solar, Blinds
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